Antenna system



Jiily 28, 1942. N. p. CASE 2,291,450

ANTENNA SYSTEM Filed Dec. 28, 1939 b L WAVE SIGNAL 10 RECEIVER &

INVENTOR ELmN P. CASE ATTORNEY Patented July 28, 1942 ANTENNA SYSTEMNelson P. Case, Great Neck, N. Y., assignor t Hazeltine Corporation, acorporation of Dela- Ware Application December 28, 1939, Serial No.311,374

11 Claims.

This invention relates to antenna systems and particularly to loopantenna systems for selectively receiving Wave signals in differentfrequency ranges.

It is a well-known fact that a loop antenna essentially is a coil oflarge area. A radiated wave signal induces a voltage in the circuit ofthe loop antenna that varies in amplitude with the orientation of theloop antenna with respect to the wave front; that is to say, when theplane of the loop antenna is parallel to the direction of wave-signaltravel and normal to the direction of the magnetic field, the wave frontreaches the two sides of the coil at slightly different times, causing aphase difference in the voltages induced therein that gives rise to aresultant voltage acting around the circuit of the loop.

For receiving wave signals in two different frequency ranges, such asthe so-called broadcast frequency range and the so-called short-wavefrequency range, it has heretofore been proposed to utilize a singlecoil loop antenna tuned by a single tuning condenser and having a tapdividing the loop into two sections, each tunable by the condenser toWave signals in its respective frequency range. However, such a tappedloop antenna inherently has certain disadvantages; for example, when anunused loop antenna section is short-circuited during the operation ofan active loop antenna section in its respective frequency range, theshort-circuited loop antenna section acts as a shield which impairsoperation of the active loop antenna section.

Another disadvantage of loop antenna arrangements of the prior art isthat of undesirable sensitivity to local noise, resulting from naturaland man-made electrical disturbances.

It is an-object of this invention, therefore, to provide an improvedloop antenna system which overcomes the foregoing undesirable featuresof the prior art and which is simple and economical in its parts andefficient and effective in operation.

It is another object of the invention to provide an improved loopantenna system which is selectively tunable to wave signals in differentfrequency ranges.

It is a further object of the invention to provide a loop antenna systemcomprising several antenna sections which are responsive to wave signalsand are tunable to given frequency ranges and wherein one antennasection is caused to provide an interference-reducing shield 'for theactive antenna section.

In accordance with one embodiment of the in- '55 vention, an antennasystem selectively operable over a plurality of carrier-wave frequencyranges comprises a plurality of antenna sections each having theproperty of directional response and each adapted to be tuned to carriersignals in its respective frequency range. The antenna sections are sooriented relative to each other that their respective directions ofresponse form a relatively large angle. The system includes means foreffectively selecting one of the sections to receive desired carriersignals in its respective frequency range and for conditioning anotherof the sections "to reduce over the frequency range of the one sectionthe intensity of received wave signals arriving at the antenna systemfrom directions other than the direction of maximum response of the onesection, whereby the other section is effective to provide aninterferencereducing shield for the one section.

In accordance with a particular form of the invention, in an antennasystem of the type described, antenna means selectively tunable to wavesignals in three different frequency ranges comprises three loop antennasections each directionally responsive to wave signals in its respectivefrequency range. The loop antenna sections are disposed in planes havingrelatively large angles to each other, one of the planes intersectingthe line of intersection of the other two planes at a large angle. Theantenna means includes means for tuning one of the loop antenna sectionsto desired wave signals in its respective frequency range, and means forrendering others of the loop antenna sections effective to absorbcarrier-signal energy over the frequency range of the one antennasection, whereby the other loop antenna sections effectively provide aninterference-reducing shield for the one loop antenna section.

For a better understanding of the present invention, together with otherand further objects thereof, reference is bad to the followingdescription taken in connection with the accompanying drawing and itsscope will be pointed out in the appended claims.

In the accompanying drawing, Fig. 1 is a perspective view of an antennasystem embodying the present invention; Fig. 2 is a circuit diagram,partly schematic, of a wave-signal receiver including the antenna systemof the invention; Fig. 3 is a perspective view of another antenna systemcomprising a modified form of the invention; Fig. 4-is a plan Viewillustrating the operation of the invention; and Fig. 5 is a circuitdiagram of an antenna system embodying the antenna of Fig. 3.

Referring now more particularly to Fig. l of the drawing, there isillustrated, in an antenna system If], antenna means adapted to beselectively tunable to wave signals in different frequency ranges. Thismeans comprises a plurality of loop antenna sections, specifically anantenna section I I of relatively high inductance and an antenna sectionI2 of relatively low inductance, each responsive to wave signals in itsrespective frequency range and mounted on any suitable support I3 forrotation about a vertical spindle I4. The antenna section II consists ofa coil of a plurality of turns responsive to modulated carrierwavesignals in the broadcast range of frequencies, for example. The antennasection I2 is arranged on the outside of the section II in a planesubstantially at right angles thereto and consists of two turns of metaltubing, such as copper, to provide a coil responsive to modulatedcarrier-wave signals in a higher frequency range, for example. The twosections II and I2 of the antenna Ill are connected in series relationand are provided with a common terminal b and end terminals a and c.

Referring now to Fig. 2 of the drawing, there is represented a circuitdiagram, partly schematic, of a complete wave-signal receiver includingthe antenna system of the invention. The common terminal I) of the loopsections I I and I2 is coupled through a normally open switch I5 to aterminal of the antenna section II for shortcircuiting the latter, asdesired. The antenna sections II and I2 are coupled through terminals aand c to a conventional tuning condenser Hi to form the tunable inputcircuit of a wave-signal receiver I! of any suitable type, such as asuperheterodyne receiver, the output of which is delivered to asound-reproducing unit I8.

In considering the operation of the present invention, reference is hadto Fig. 4 of the drawing, it being assumed that the switch I5 is closedto short-circuit the section I I and that the receiver is tuned to anydesired station 23, the antenna I!) being in the position indicated bydotted lines with respect to the direction of travel 24 of the desiredsignals from the station 23. In this position of the antenna It], theselected section I2 is not in a position parallel with direction oftravel 24 of the desired signals and intercepts but a fraction of theavailable signal strength; while the nonselected section 5 I is not in aposition normal to the wave front so that it also intercepts andeffectively partially absorbs the desired wave signals. Hence, theoutput of the receiver is even lower than it would he were thenonselected antenna section I I not present. However, as the antenna I6is adjusted about its axis of rotation to orient the selected section I2so that its plane is parallel to the direction of travel 24 of thedesired wave signal in its frequency range, the signal pick-up of theselected section I2 increases and the absorption by the nonselectedsection II simultaneously decreases so that the output of the receiverincreases rapidly to a maximum value. Thus, the nonselected section IIimparts to the selected section I2 a sharply-directional characteristicso that the selected section may be readily adjusted as nearly inparallel relation with the direction of travel of the desired signals asis consistent with conditions of reception, for example, noiseinterference. In such position of the antenna II], with the plane of theselected shortwave antenna section l2 in substantially parallel relationto the direction of travel 24 of the wave signal, a maximum signalvoltage is induced therein, the short-circuited section II beingdisposed in a vertical plane substantially parallel to the signal-wavefront, that is to say, at right angles to the direction of travel of thewave signal. In this way, the nonselected section II not only does notimpair operation of the selected section I2 but reduces undesirableinterference, particularly noises arising from nearby sources andinterfering signals from other directions, such as signals radiated fromstations 26 and 21 having directions of travel 28 and 29, respectively,angularly related to the plane of the selected section I2.

When one antenna section is active and properly oriented with respect tothe direction of travel of the desired wave signals, the nonselectedsection effectively shields the active section from all undesirableinterference originating from stations in directions different from thesource of desired signals, except that no reduction is effected in theinterference produced by an undesired station located exactly degreesfrom the desired station. Coupling between the selected and nonselectedsections is maintained at a minimum by virtue of their physical relationwith respect to each other. The shielding effect of the nonselectedsection is due primarily to its action as a trap for noise which mightotherwise interfere with the desired signals to which the selectedsection is properly tuned and oriented.

For broadcast band reception, the switch I5 is left open and theoperation of the system is similar to that described above except forthe absence of the directional and shielding eifects. However, if sucheffect is necessary or desired, it may be obtained by short-circuitingthe antenna section I2 during operation with the broadcast band sectionII.

From the foregoing description of the invention, it will be seen thatthe condenser I6 comprises means for tuning one of the loop antennasections, for example the antenna section I2 of lower inductance, towave signals in a desired frequency range and the switch I5 comprisesmeans for effectively short-circuiting the other loop antenna section,for example the antenna section II of higher inductance, to conditionsuch other loop section I I to reduce over the frequency range of theone section I2 the intensity of received wave signals arriving at theantenna system from directions other than the direction of maximumresponse of the one section I2, whereby the other loop-antenna sectionII effectively provides an interference-reducing shield for the one loopantenna section I2.

Referring to Fig. 3, a modified form of the invention is embodied in theantenna system 2|] which comprises a loop antenna section M in ad ditionto the two sections II and I2 corresponding to those of antenna systemIII and lying in a plane perpendicular to the planes of both suchantenna sections. As thus arranged, the sections II and 2I lie insubstantially vertical planes and the section I2 lies in a substantiallyhorizontal plane. The section 2| is selectively tunable to wave signalsin a different frequency range from that of either of sections II andI2. The circuit arrangement of the modification of Fig. 3, asrepresented in Fig. 5, is essentially similar to that of Fig. 2 andsimilar circuit elements are designated by similar reference characters.In this modification, the switch 30 is of a conventional constructionwhich is effective selectively to connect any one of the loop-antennasections H, 2!, and 12, across the tuning condenser |6 while, at thesame time, shorting out of circuit the remaining two antenna sections.The operation of this embodiment will be understood from the detaileddescription of that of the embodiment of Figs. 1 and 2 without furtherelaboration here except to point out that the loop antenna sections areseries-connected and progressively increase in inductance, each of thethree antenna sections being responsive and tunable to a separateindividual frequency range. The circuit arrangement is such that the twosections not being used in the reception of a desired signal wave areshort-circuited to provide interference-reducing shields for the activesections used in the reception of the desired signal wave. However, whena high-frequency section is active, a nonadjacent low-frequency sectionneed not be physically shorted; for example, when the highest-frequencysection I2 is active, the inherent capacitance of the lowest-frequencysection II effectively short-circuits it at frequencies within thehigh-frequency range.

When the loop antenna sections II, M, Fig. 1, or I I, I2 and 24, Fig. 3,are so oriented relative to each other that their respective directionsof response form a relatively large angle as described, the selectedsection has a maximum directional response in the direction of the planein which it lies due to the efiect of a nonselected section or sectionsin providing maximum shielding effect for undesired wave signalsarriving at the antenna section from a direction forming a large anglewith the direction of arrival of desired wave signals.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is, therefore,aimed in the appended claims to cover all such changes and modificationsas fall within the true spirit and scope of the invention.

What is claimed is:

1. An antenna system selectively operable over a plurality ofcarrier-wave frequency ranges comprising, a plurality of antennasections each having the property of directional response and eachadapted to be tuned to carrier signals in its respective frequencyrange, said antenna sections being so oriented relative to each otherthat their respective directions of response form a relatively largeangle, and means for effectively one of said sections to receive desiredcarrier signals in its respective frequency range and for conditioninganother of said sections to reduce over the frequency range of said onesection the intensit of received wave signals arriving at said antennasystem from directions other than the direction of maximum response ofsaid one section, whereby said other section is effective to provide aninterference reducing shield for said one section.

2. An antenna system selectively operable over a plurality ofcarrier-wave frequency ranges comprising, a plurality of loop-antennasections, each having the property of directional response and eachadapted to be tuned to carrier signals in its respective frequencyrange, said loop-antenna sections being so oriented relative to eachother than their respective directions of response form a relativelylarge angle, and means for cffectively selecting one of said loop.sections to receive desired carrier signals in its respective frequencyrange and for conditioning another of said loop sections to reduce overthe frequency range of said one section the intensity of received wavesignals arriving at said antenna system from directions other than thedirection of maximum response of said one section whereby said otherloop section is effective to provide an interference-reducing shield forsaid one loop section.

3. In an. antenna system, antenna means selectively tunable to Wavesignals in different frequency ranges comprising, a plurality of loopantenna sections each responsive to wave signals in its respectivefrequency range, at least two of said loop antenna sections beingdisposed in planes substantially at right angles to each other, meansfor tuning one of said two loop antenna sections to wave signals in adesired frequency range, and means for conditioning the other of saidtwo loop antenna sections to reduce over the frequency range of said onesection the intensity of received Wave signals arriving at said antennasystem fromdirections other than the direction of maximum response ofsaid one section, whereby said other loop antenna section effectivelyprovides an interference-reducing shield for said one loop antennasection.

4. In an antenna system, antenna means selectively tunable to wavesignals in different frequency ranges comprising, a pair of loop antennasections of different inductance each responsive to wave signals in itsrespective frequency range, said loop antenna sections being disposed inplanes substantially at right angles to each other, means for tuning theloop antenna section of lower inductance to wave signals in a desiredfrequency range, and means for conditioning the loop antenna section ofhigher inductance to reduce over the frequency range of said antennasection of lower inductance the intensity of received wave signalsarriving at said antenna system from directions other than the directionof maximum response of said antenna section of lower inductance, wherebysaid loop antenna section of higher inductance effectively provides aninterference reducing shield for said loop antenna section of lowerinductance.

5. In an antenna system, antenna means selectively tunable to wavesignals in different frequency ranges comprising, a pair ofseries-connected loop antenna sections of different inductance eachresponsive to wave signals in its respective frequency range, said loopantenna sections being disposed in planes substantially at right anglesto each other, means for tuning the loop antenna section of lowerinductance to wave signals in a desired frequency range, and means foreffectively short-circuiting said loop antenna section of higherinductance, whereby said loop-antenna section of higher inductanceeffectively provides an interference-reducing shield for saidloop-antenna section of lower inductance.

6. In an antenna system, antenna means selectively tunable to wavesignals in different frequency ranges comprising, a pair of loop antennasections connected in series one of which is responsive to wave signalsin a broadcast frequency range and the other of which is responsive towave signals in a higher-frequency range, said loop antenna sectionsbeing disposed in planes substantially at right angles to each other,means for tuning one of said loop antenna sections to wave signals in adesired frequency range, and means for effectively short-circuiting theother of said loop antenna sections, whereby said other loop antennasection effectively provides an interference-reducing shield for saidone loop antenna section.

7. In an antenna system, antenna means selectively tunable to wavesignals in three different frequency ranges comprising, three loopantenna sections each responsive to wave signals in its respectivefrequency range, said loop antenna sections being disposed in planes atright angles to one another, means for tuning one of said loop antennasections to wave signals in a desired frequency range, and means foreffectively short-circuiting the others of said loop antenna sections,whereby said other antennaisections effectively provide aninterference-reducing shield for said one loop-antenna section.

8. In an antenna system, antenna means selectively tunable to wavesignals in three different frequency ranges comprising, threeseries-connected loop antenna sections of progressively increasinginductance each responsive to wave signals in its respective frequencyrange, said loop antenna sections being disposed in planes at rightangles to one another, means for tuning one of said loop antennasections of lower inductance to wave signals in its respective frequencyrange, and means for effectively shortcircuiting at least one of theloop antenna-sections of higher inductance than said one section,whereby said one section of higher inductance effectively provides aninterference-reducing shield for said one section of lower inductance.

9. In an antenna system, directionally adjustable antenna meansselectively tunable to wave signals in different frequency rangescomprising, a plurality of loop antenna sections, each responsive towave signals in its respective frequency range, at least two of saidsections being disposed in vertical planes substantially at right anglesto each other, said sections being rotatable about a vertical axis fororienting a selected one of said sections so that its plane is parallelto the direction of travel of desired wave signals in its frequencyrange, means for tuning the selected section to wave signals in thedesired frequency range, and means for effectively short-circuiting theother of said two sections, whereby, in orienting the selected sectionwith respect to the direction of travel of the desired wave signals,said other section efiectively partially absorbs the delected section,whereby,

sired wave signals when the selected section is not exactly oriented,thereby to impart a sharplydirectional characteristic to the selectedsection and the effect of said other section on the selected sectionbeing such, when the selected section is properly oriented, that thesaid other section provides an effective interference-reducing shieldfor the selected section.

10. In an antenna system, antenna means selectively tunable to wavesignals in three different frequency ranges comprising, threeloop-antenna sections each directionally responsive to wave signals inits respective frequency range, said loopantenna sections being disposedin planes having relatively large angles to each other, on of saidplanes intersecting the line of intersection of the other two planes ata large angle, means for tuning one of said loop-antenna sections todesired wave signals in its respective frequency range, and means forrendering the others loop-antenna sections effective to absorbcarriersignal energy over the frequency range of said one antennasection, whereby said other loopantenna sections eifectively provide aninter- -ference-reducing shield for said one loop-antenna section.

11. In an antenna system, directionally-adjustable antenna meansselectively tunable to wave signals in different frequency rangescomprising, three loop-antenna sections each responsive to wave signalsin its respective frequency range, two of said sections being disposedin vertical planes substantially at right angles to each other and thethird of said sections being disposed in a substantially horizontalplane, said verticallydisposed sections being rotatable about a verticalaxis for orienting a selected on of said verticallydisposed sections sothat its plane is parallel to the direction of travel of desired wavesignals in its frequency range, means for tuning a selected one of saidsections to desired wave signals in its respective frequency range, andmeans for rendering the others of said sections effective to provide aninterference-reducing shield for said sein orienting said selectedsection with respect to the direction of travel of the desired wavesignals, at least one of th nonselected sections effectively partiallyabsorbs the desired wave signals when the selected section is notexactly oriented, thereby to impart a sharplydirectional characteristicto said selected section.

NELSON P. CASE.

of said

